Guptill said teammate Corey Anderson didn't think he had edged the ball yesterday which had Pakistan in despair late in the chase.
It was a crucial decision by umpire Brent Bowden and with Anderson smearing the next two deliveries from luckless Wahab Riaz for six, it rushed New Zealand towards their target.
The win was achieved with two balls to spare, demonstrating the importance of that decision.
"'Cozza' said he didn't realise he'd hit the ball. That can happen sometimes.
"I've had times I've been given out caught behind and didn't realise I'd hit it. It's all swings and roundabouts."
Australia are in town, ahead of the start of their three-game ODI series, also at Eden Park, on Wednesday.
Guptill said thinking and planning will start today, as the focus had been on the Pakistanis while their six-game tour was on.
"We haven't spoken about it, but talking to people, they're excited about Australia coming."
Guptill was the world's top runmaker in ODI cricket last year and carried on in similar vein in January with 222 runs in four innings.
He isn't about to start tinkering on specifics with Australia's bowling attack in mind.
"You don't really have to change a lot," he said.
"Just keep being positive and keep preparing well. The only thing we can control is how we prepare, and you hope to score a few runs."